The invention relates to a method and an apparatus for the control of fuel injection signals to be used with the fuel injection system of an internal combustion engine. The intermittent injection control signals have a minimum duration and the fuel injection system includes a first pulse generator circuit which generates preliminary pulses proportional to the aspirated air quantity and rpm. The system includes a multiplying circuit connected in series with the pulse generator circuit and both of these circuits contain capacitors which control multivibrators.
It is known to provide an electronic fuel injection system in which the duration of the control pulses for the various fuel injection valves is determined substantially from the load of the engine at any given time and the instantaneous rpm. A circuit, which will be explained in more detail below, uses these two variables to provide a so-called preliminary pulse. However, when the variables which define the duration of these pulses, i.e., the rpm and the load, assume unfavorable values, for example, if the rpm is very high and the load very small, for example during downhill operation, the duration of the control pulses can be so short that it results in a critical fuel metering in which the fuel mixture no longer is able to sustain combustion in the cylinder. Such a condition is very undesirable in internal combustion engines that employ exhaust gas purifiers, for example catalyzers or after-burners, because the uncombusted fuel can cause substantial damage to these devices.